Hi,
it's corect. Nat is not supported in 12.2(20). You can see that the Nat Commands are unsupported:
Network Address Translation (NAT) Commands
Unsupported User EXEC Commands
clear ip nat translation
show ip nat statistics
show ip nat translations
Unsupported Global Configuration Commands
ip nat inside destination
ip nat inside source
ip nat outside source
ip nat pool
Unsupported Interface Configuration Commands
ip nat
URL:http://www.cisco.com/en/US/partner/products/hw/switches/ps5023/products_configuration_guide_chapter09186a008021272e.html#wp1021398
Regards
Peter